The invention relates to a method to process metal surfaces.
In a well-known procedure to produce a coarsely cratered structure in a metal embossing surface of embossing roller, first a silicone cast is made from a natural pattern and as a result the negative of the coarsely cratered structure is present on the surface of this cast, whereupon a positive of the coarsely cratered structure is made by new casting and the surface of this positive is provided with an electrically conductive coating onto which a metal layer, in general nickel, is deposited by plating. Following plating, the positive is removed and thereby the metal embossing surface with the negative of the pattern""s coarsely cratered structure is exposed. Endowing the embossing surface thereafter with a fine structure by particle-blasting treatment or etching or the like in order to render it matte, for imparting the look of natural leather, is known.
It was found that a product embossed by such an embossing surface differs from a natural product in that the appearance of the natural pattern is not imparted.
The German patent document A1 196 36 801 discloses a procedure of the kind cited in the preamble of claim 1 wherein a steel band is moved through several processing chambers containing sand blasters acting on the surface of the band. The blaster effect is enhanced by the multiple exposures to the blasters. The different sand blasters do not produce a varying sand blasted effect.
The objective of the invention is to create a method of the kind cited in the preamble of claim for the processing of a metal surface with which a product can be embossed, in which the surface more closely resembles the natural pattern.
The basic concept of the invention is to provide the surface for forming an embossing surface with a coarsely cratered structure, and to provide the peaks and troughs of this structure with different fine cratered structures, i.e., different depths of roughness, whereby greater similarity is achieved between the embossed surface and the surface of a pattern, for instance natural leather. For this purpose, the entire embossing surface having the coarsely cratered structure is provided in the invention with a finely cratered structure of a first depth of roughness, whereupon the surface provided with a finely cratered structure of the first depth of roughness receives a protective coating which protects the embossing surface in the region of the troughs when, in a further method stage, the peaks of the coarsely cratered structure are provided by particle blasters or etching or the like with a finely cratered structure of a second depth of roughness. Following removal of the protective coating from the troughs, the embossing surface has the structure according to the invention, wherein the peaks and troughs have different finely cratered structures, that is depths of roughness or degrees of gloss.
Various surface appearances can be achieved using this method according to the invention. The depth of roughness may vary and either the peaks may be provided with a finely cratered structure of less depth of roughness than the troughs, or vice-versa.
In an advantageous embodiment of the invention, the protective coating is deposited across the peaks and troughs of the coarsely cratered structure and thereafter the protective layer is removed around the peaks of the coarsely cratered structure. Advantageously such removal can be implemented by wiping or scraping, preferably using means softening this protective coating.